Generally, a mobile communication system is configured to monitor a synchronization state between a radio base station and a mobile station. For example, in a mobile communication system of the WCDMA scheme, the following two criteria are defined to determine a downlink synchronization state in a physical layer.
Radio quality (DPCCH quality) of DPCCH (Dedicated Physical Control Channel); and
CRC (Cyclic redundancy check) check result
Here, the “DPCCH quality” corresponds to a reception quality of pilot symbols or TPC (transmission power control) bits, for example, an SIR (signal-to-interference power ratio) or a reception level, and the “CRC check result” corresponds to a block error rate.
That is, the mobile station determines the synchronization state of the downlink based on the radio quality of DPCCH, for example.
By the way, generally, in the mobile communication system, a test is applied to the mobile station and the radio base station in order to ensure the communication quality.
With reference to FIG. 1, a test method of confirming the determination operation of the synchronization state of the downlink in the mobile station of the above-described WCDMA scheme will be explained, below.
In FIG. 1, “DPCCH_Ec/Ior” is a power level of DPCCH, and corresponds to the radio quality of DPCCH. Further, “Qin” and “Qout” are threshold values used for determining the synchronization state of the downlink.
In this case, a state where the synchronization state of the downlink is OK may be referred to as “In-sync (In-Synchronous)”, and a state where the synchronization state of the downlink is NG may be referred to as “Out-of-sync (Out-of-Synchronous)”.
Moreover, a state where a problem of a radio link state is not detected may be referred to as “In-sync”, and a state where the problem of a radio link state is detected may be referred to as “Out-of-sync”.
In the test method illustrated in FIG. 1, at time B, the radio quality of DPCCH is changed from a state where it is higher than a predetermined threshold value Qout to a state where it is lower than the same, and at time C, it is confirmed based on the fact that the mobile station stops an uplink signal that the mobile station correctly determines the synchronization state of the downlink.
That is, when detecting Out-of-sync, the mobile station performs an operation to stop the uplink signal, and therefore, if the operation that the mobile station stops the uplink signal is confirmed at time C, then it can be confirmed that the mobile station correctly detects the Out-of-sync.
It is noted that a time difference from time B to time C is set in order to consider a determination delay in the mobile station.
On the other hand, based on the fact that at time E, the radio quality of DPCCH is changed from a state where it is lower than a predetermined threshold value Qin to a state where it is higher than the same, and at time F, the mobile station transmits the uplink signal, it is confirmed that the mobile station correctly determines the synchronization state of the downlink.
That is, when detecting In-sync, the mobile station performs an operation of starting the transmission of the uplink signal, as a result of which at time F, if the operation that the mobile station transmits the uplink signal is confirmed, then the correct detection of In-sync by the mobile station can be confirmed.
It is noted that a time difference from time E to time F is set in order to consider a determination delay in the mobile station.
As described above, in a test method of confirming the determination operation of the synchronization state of the downlink of the mobile station of the WCDMA scheme, the correct determination operation of the synchronization state of the downlink by the mobile station is confirmed based on the fact that the radio quality of DPCCH is varied, and when the radio quality of DPCCH becomes equal to or less than Qout, the mobile station stops transmitting the uplink, and when the radio quality of DPCCH becomes equal to or more than Qin, the mobile station starts transmitting the uplink.
However, there is a case where the above-described test method cannot be applied to a certain mobile communication system.
In the LTE (Long Term Evolution) scheme that is a next generation to the WCDMA scheme, for example, the mobile station stops the uplink signal not at a time point at which the synchronization state of the downlink is determined in a physical layer but at a time point at which a failure of the radio link state is determined in an RRC layer.
At this time, the mobile station starts a process of re-establishing a connection state from the time point at which the failure of the radio link state in the RRC layer is determined, and thus, there is a problem that the test method illustrated in FIG. 1 cannot be applied.
More specifically, at time C in FIG. 1, the mobile station has started the process of re-establishing a connection state at the time point at which it is confirmed that the transmission of the uplink signal is stopped, and therefore, even when the radio quality of DPCCH is larger than Qin at time E, the mobile station does not start transmitting the uplink signal. As a result, the test method illustrated in FIG. 1 cannot be applied.
Therefore, the present invention is intended to overcome the above-described problem. An object of the present invention is to provide a test method and a test device that enable confirmation of whether a mobile station correctly detects a synchronization state of a downlink, even upon starting a process of re-establishing a connection state at a time point at which a failure of a radio link state is detected in an RRC layer.